1. Field of Invention
The present invention relates to a switching regulator, a switching regulator driver circuit, and a switching regulator control method; particularly, it relates to a switching regulator which is controlled to operate in or near boundary conduction mode (BCM), and a driver circuit and a control method which operate a switching regulator in or near BCM.
2. Description of Related Art
FIG. 1 shows the circuitry of a typical switching regulator, in which a PWM (pulse width modulation) controller 11 controls one or more power transistors in a power stage circuit 12, to convert an input voltage Vin to an output voltage Vout or output current Iout. The power stage circuit 12 may be, but is not limited to, asynchronous or asynchronous buck, boost, inverting or buck-boost converter as shown in FIGS. 2A-2H. Back to FIG. 1, a feedback circuit 13 generates a feedback signal relating to the output voltage Vout or the output current Iout and sends the feedback signal to the PWM controller 11 so that the PWM controller 11 can control the power stage circuit 12 to regulate the output voltage Vout or the output current Iout to a desired target.
FIG. 3 shows a switching regulator which generates two output voltages Vout1 and Vout2, with two feedback control circuits: the first feedback circuit 13A and the second feedback circuit 13B. The power stage circuit 12 in this case may be, but is not limited to, a synchronous or asynchronous inverting-boost converter as shown in FIGS. 4A and 4B.
FIGS. 5A-5C show three operation modes of a switching regulator, taking the asynchronous boost switching regulator of FIG. 2D as an example. As shown in FIG. 5A, in continuous conduction mode (CCM), the power transistor is turned ON before the inductor current I(L) decreases to zero. This causes larger switching loss and higher EMI (electro-magnetic interferences), especially in high voltage applications. In discontinuous conduction mode (DCM) as shown in FIG. 5C, to supply required power to the output, it requires a higher peak current and therefore it requires a power transistor with higher current rating, causing higher conduction power loss.
Therefore, in many applications, it is best to operate the switching regulator in boundary conduction mode (BCM) as shown in FIG. 5B.
In view of the foregoing, the present invention provides a switching regulator which is controlled to operate in or near BCM, and a switching regulator driver circuit and a switching regulator control method to operate a switching regulator in or near BCM.